Electrophotographic developing method and apparatus

ABSTRACT

In an electrophotographic developing apparatus where developing electrode rollers are disposed above driving rollers, and an electrophotographic sheet bearing an electrostatic latent image is passed therebetween the driving rollers are spaced, and in the spaces between the driving rollers other rollers are uniformly disposed to form with the driving rollers and with sideplates, a reservoir of liquid developer which is applied from above the latent image bearing sheet. Upon passage of the latent image bearing sheet between the rollers and through the liquid reservoir, development occurs. The method of developing comprising passing said latent image bearing sheet through such a developer reservoir.

United States Patent [191 Fukushima Dec. 17, 1974 ELECTROPHOTOGRAPHIC DEVELOPING [73] Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: Dec. 30, 1971 [21] Appl. No.: 214,247

[30] Foreign Application Priority Data Dec. 30, 1970 Japan 45-122800 [52] US. Cl 117/37 LE, 118/637, ll8/D1G. 23 [51] lnt.C1. G03g 13/10, G03g 15/10 [58] Field oi Search 117/37 LE; 96/1 LY; ll8/D1G. 23, 637; 355/10; 95/89 R, 95, 94

[56] References Cited UNITED STATES PATENTS 3,301,156 1/1967 Roeber 95/89 R 3,381,662 5/1968 Kolb et al7 117/37 LE 3,575,101 4/1971 Smith 5/94 Miller 117/37 LE Sato et a1 118/637 Primary Examiner-Michael Sofocleous Attorney, Agent, or FirmJ. T. Martin; Gerald J. Ferguson, Jr.; Joseph J. Baker 5 7 ABSTRACT In an electrophotographic developing apparatus where developing electrode rollers are disposed above driving rollers, and an electrophotographic sheet bearing an electrostatic latent image is passed therebetween the driving rollers are spaced, and in the spaces between the driving rollers other rollers are uniformly disposed to form with the driving rollers and with sideplates, a reservoir of liquid developer which is applied from above the latent image bearing sheet. Upon passage of the latent image bearing sheet between the r01- lers and through the liquid reservoir, development occurs. The method of developing comprising passing said latent image bearing sheet through such a developer reservoir.

5 Claims, 6 Drawing Figures mu 2 m 4 FIG. 2

PATENTEB DEC] 7 I974 FIG. 3

IOBLI PATENTEL SEC 1 7 I974 FIG. 5

PATENTELSEC 11914 sum u or 4 FIG. 6

ELECTROPHOTOGRAPHIC DEVELOPING METHOD AND APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method and apparatus for electrophotography, more particularly to a method and apparatus for obtaining a visible image using a developer on a flexible electrophotographic sheet material.

2. Description of the Prior Art According to conventional electrophotography, the following means and procedures are employed for obtaining a visible image on a flexible material sheet using a liquid developer. First, a sheet of flexible material such as paper, plastic or the like, is subjected to an electroconductization treatment, and on this sheet is provided a photoconductive layer of metal such as selenium (Se) by vapor deposition or other means, or a layer of inorganic photoconductive powder, e.g., zinc oxide, cadmium fluoride, titanium oxide or the like, mixed with resin, to thereby obtain an electrophotographic sheet material. The thus obtained electrophotographic sheet material is uniformly electrically charged by charging means, such as corona discharge means in the dark, and then the material is image exposed, whereby the charge is attenuated according to the amount of light applied during exposure and, con:

sequently, a charge pattern (electrostatic latent image) conforming to the light and shade of the image is formed on the electrophotographic sheet material. The sheet is then contacted with a liquid developer prepared by dispersing colored charged grains (hereinafter referred to as toner) in an insulating liquid, so as to deposit the toner in conformity with the charge pattern, thereby obtaining a visible image corresponding to the original. After development, the image may be fixed by suitable means to obtain a stable reproduction of the original.

There are also known other methods, such as for instance electrostatic printing methods, for obtaining an electrostatic latent image. However, when development is conducted using such known methods, the toner in the developer is attracted by the electric lines of force extending into the developer, and is thereby deposited on the electrostatic latent image. However, since no electric line of force comes out above certain parts of the latent image according to the pattern of said image. edge effect takes place, resulting in a developed image far removed from the original.

It is also known to provide an electroconductive object in opposition to the surface of the electrostatic latent image to reduce the edge effect and make the density pattern of the electric lines of force approach the pattern of the electrostatic latent image. This technique is based on the fact that the electroconductive object increases the number of the electric lines of force from the electrostatic latent image and also absorbs them to make the density pattern of the electric lines of force approach the pattern of the electrostatic latent image. This effect is called the developing electrode effect. The smaller the specific resistance of the developing electrode and the smaller the distance between the electrode and the latent image surface, the greater the developing electrode effect. Therefore, when conducting development with a liquid developer, the developer must be supplied between the developing electrode and the latent image surface of the sensitive material. In this case, no matter how closely the developing electrode approaches the latent image surface, if the liquid supply or exchange is insufficient, there will be a shortage or non-uniform supply of the toner, resulting in a shortage or unevenness of development. Thus, there is need for an apparatus which has a high developing electrode effect and which always allows a sufficient supply and exchange of liquid.

Other problems that are encountered along with the edge effect in performing development of an electrostatic latent image trailing" and liquid supply unevenness mentioned before.

Trailing" is caused when the toner, without being deposited faithfully to the charge distribution in the electrostatic latent image, is deposited like the trail of a comet extending from the high-density portion to the low-density portion, particularly at parts where a highdensity portion and a low-density portion are closely adjacent to each other. It is believedtrailing is causes as follows. When the developer moves between the latent image surface and the developing electrodes at a relative velocity with respect to the latent image surface, the toner, although receiving an attractive force from the latent image, is urged by the flow of the developer to flow downstreamv of the image and deposit downstream. It is also known that when the toner velocity relative to the latent image surface is the same as the developer velocity, the size of such trailing streaks is enlarged proportionally to the extent of the developing electrode effect.

Another problem encountered in the development of an electrostatic latent image is liquid supply unevenness. It is extremely difficult to uniformly supply developer to the latent image surface, and even admitting that such uniform supply could be achieved, if the amount of supply is insufficient, the toner density will become deficient to cause imperfect development in the high-density portions, resulting in unevenness of development. Thus, the supply of the developer must be conducted uniformly and sufficiently.

The time spent for the development must be minimized, for, otherwise, the changes forming the latent image will be attenuated and residual charges will be developed. Attenuation ofthe latent image is caused by deposition of components of the developer other than the toner on the surface of the electrophotographic material, or by leakage of charge into the sensitive material. Normally, it is desirable that all of the charges in the latent image be neutralized by deposition of the toner alone, but should such attenuation take place,

toner deposition is reduced by an amount corresponding to the extent of such attenuation, thus making it impossible to perform development faithfully to the charge distribution. Elongated developing time invites a greater attenuation of the latent image.

The term residual Potential in the electrophotography art means the surface potential due to charges which remain at a higher value than the ideal range. Normally, such charges must sufficiently be attenuated by exposure. Thus, the absolute value of the density distribution of the original does not necessarily correspond to that of the potential distribution of the electrostatic latent image. if the developing time is long, such residual potential may also occur.

Elongated developing time is also undesirable from the viewpoint of speedy and efficient treatment.

It is thus absolutely required for high-fidelity reproduction of a photographic image, particularly one of contiuous gradation, to develop the electrostatic latent image within a minimum span of time, without producing any edge effect, trailing or unevenness of development and also without allowing residual potential to be developed.

As will be apparent from the foregoing discussion, incompatible conditions are needed to solve all of these problems. For instance, in order to eliminate the edge effect, it is required to enhance the developing electrode effect, but if the developing electrodes approach the latent image surface for achieving such enhancement of the electrode effect, it becomes more difficult to carry out feed and exchange of liquid resulting in causing unevenness of liquid supply. Ifthe liquid supply is accelerated to overcome such a defect, liquid velocity relative to the latent image surface is increased, resulting in the possibility of trailing." There is also a tendency that the closer the developing electrode is to the latent image surface the higher the possibility of producing trailing. Further, an attempt to solve such problems by allowing a longer process time results in increased attenuation of the latent image and fogging due to residual potential.

SUMMARY OF THE INVENTION The present invention is to provide an electrophotographic developing method and apparatus which does not give rise to an edge" effect in the developed image, which produces no unevennness of development that may be due to non-uniform supply of the developer (called unevenness of liquid supply"), is not subject to the phenomenon of creating a comet trail-like streak of blot running from a high-density part of the image to a low-density part (called image trailing").

The apparatus of this invention is also small in size and simple in structure so that it may be conveniently incorporated into an automatic electrophotographic device, and it is easy to manufacture and maintain.

An apparatus is also provided which suited for ob taining a high-fidelity reproduction of a photographic image of continuous gradation on a flexible electrophotographic material sheet.

According to the present invention, rotatable rollerlike developing electrodes are used to allow sufficient feed and exchange of liquid and to eliminate the edge effect. According to this arrangement, each part of the latent image bearing surface coming under one developing electrode always encounters a fresh rotating surface of the electrode rollers, since the image bearing surface and developing electrode are driven by each other without slipping. Therefore, the effect of the developing electrode is uniform over the entire surface of the sheet to be developed, and the resulting developed image has a high degree of uniformity.

Narrow endless belts are provided along both edges of the sensitive material strip to drive said strip and to allow the roller-like developing electrodes to be located in opposition to and in slight and uniformly spaced-apart relation with the latent image surface. If the development is conducted by contacting the developing electrode rollers directly against the latent image surface, the latent image or developed toner image is rubbed by the developing electrode rollers and may be worn or destroyed. According to the present invention.

there is no such fear because the rollers are arranged slightly spaced-apart from the latent image surface and also the rollers are rotated substantially at the same velocity as the driving velocity of the sensitive material.

Further, according to the present invention, in order to carry the sensitive material smoothly through the developing apparatus, a plurality of electroconductive rollers are arranged in ajuxtaposed relationship and rotated at the same peripheral velocity, and also the sensitive material sheet is held edgewise by the endless belts suspended round said developing electrode rollers, while the rear surface of the sensitive material is kept in contact engagement with electrically conductive driving rollers which is at ground potential. In the case where the sensitive material comprises an insulat ing backing, there may be employed endless belts Y which are in contact with the both side ends of the front surface of the sensitive material reduced its resistivity by image-exposure. The conductive endless belts which are kept at ground potential play a role of back electrode. When the sensitive material has an intermediate conductive layer between the highly insulating backing and the photoconductive coating, the intermediate layer is easily grounded by providing sharp projections on the endless belts which goes through the photoconductive coating. In this case, too, passage of the sensitive material is conducted by using a plural number of rollers. Passage by means of aroller assembly is easier to put into practical use than passage by endless belts or other like means.

Another important feature of the present invention is that the spaces between the driving rollers are filled with other rollers so as to prevent the developer, which is supplied from above, from flowing down easily between the rollers. That is to say, a liquid reservoir is formed by said other rollers. The sensitive material strip carried while being held between the endless belts and the driving rollers is passed through the thus formed liquid reservoir and thereby supplied with the developer. Formation of such a liquid reservoir inhibits the developer from being sprayed directly against the latent image surface and therefore the liquid has no large relative velocity so that no trailing nor unevenness of liquid supply is caused.

Thus, according to the present invention, it is not that the sensitive material forms a liquid reservoir to pre vent dropping of liquid only when said material is present but the sensitive material is passed through an already formed liquid reservoir. According to the method in which such a liquid reservoir is formed by the sensitive material, the situation in the mechanism is unstable until the liquid reservoir is formed, and therefore such a method is less advantageous in diminishing trailing and unevenness of liquid supply, as compared with the present invention.

Now, the present invention will be described in full detail by way of its preferred embodiments with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line IIII of FIG. ll.

FIG. 3 is a sectional view taken along line Ill-lll of FIG. I.

FIG. 4 is a schematic sectional view showing another embodiment of the present invention.

FIG. 5 is a schematic side view thereof of the embodiment of FIG. 4.

FIG. 6 is a schematic side view, with parts omitted, showing still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1, there is shown a schematic side view of an embodiment of the apparatus according to the present invention, with the side plate being removed. A sheet of sensitive material having an electrostatic latent image formed thereon is carried from a bath section in the direction of arrow 1, then passed substantially horizontally and linearly between the rollers and discharged in the direction of arrow 2 into a washing section. In the figure, numerals 3 to 10 denote the driving rollers, each being provided with a worm wheel so that they are rotated by a single worm gear. Rollers 11 to 18 are the sensitive material holding rollers which are adapted to concurrently serve as developing electrodes and so arranged as to hold both edges of the sensitive sheet material through the endless belts in the manner mentioned above to drive the sensitive sheet through friction with the driving rollers '3 to 10. The shafts of the rollers 11 18 are secured to the side plates so that the rollers can move in the vertical direction. Their lateral positions are fixed. When a sensitive material sheet is fed in, the rollers are raised up a distance equal to the thickness of said sheet and hold the sheet with the endless belts to drive the sheet through friction with the driving rollers.

FIG. 2 shows the manner in which the sensitive sheet material is held by the endless belts and in which the rollers are mounted to the side plates. Numeral 100 in the figure indicates a sensitive sheet material of which both edge portions are held by a roller 12 (in FIG. 2) through the endless belts 19. The shaft A of the roller 4 is mounted at the prescribed positions in the side plates I01, 102. Shaft portion A extends from the side plate 101 and carries at its end a worm wheel driven by a worm. B denotes a liquid check plate adapted to prevent liquid from flowing out along the shaft A. The shaft of the roller 12 is vertically movably mounted in the side plates 101 and 102. Since the bearings comprise elongated slots extending to the upper ends of the side plates, the rollers 11 18 can be removed from the top ends of the side plates without detaching the side plates. This proves extremely convenient for cleaning or other purposes. However, this arrangement involves a possibility that the liquid might leak out through the elongated slots in the side plates when the developer is reserved between the rollers, thus lowering the effect of the present device. Therefore, it is desirable to provide keeper plates 103, 104 adapted to close the elongated slots for the upper roller shafts to inhibit leakage of the liquid, thereby allowing effective preservation of the liquid in a vessel 38 for developer.

Referring now to FIG. 1, in conjunction with FIG. 2, in order to prevent the liquid from leaking out between the rollers and the side plates, it is desirable to minimize the space between (particularly) the lower rollers and the side plates, and the roller diameter is preferably kept uniform between both side plates, with no shoulders being provided on the rollers. The distance between side plates is strictly fixed by stays, and the rollers are accurately and deliberately machined to have a strictly-defined length of the uniform-diameter portions. The spacing left between the roller end and the side plate may be determined according to the extent how the developer leakage therethrough may be permitted. In case no liquid reservoir is formed when such spaces are provided, or in case trailing is produced because of increased discharge rate of liquid from the nozzles for forming the liquid reservoir, the uniformdiameter portions of the rollers 3 10 may be fitted in the side plates to provide liquid seals. Numerals 20 to 24 designate auxiliary rollers for liquid temporary accumulation which are located in the spaces between the driving rollers to prevent the liquid from flowing down directly. It is possible to minimize leakage by selecting the length of each auxiliary roller such that it is fitted between both side plates so as to produce no space therebetween.

The present invention is particularly featured by use of the auxiliary rollers for facilitating liquid reservation. Although it is possible to use means other than rollers, such as for example, flat plates, to close the gaps between the driving rollers so as to form a desired liquid reservoir, the use of rollers is most desirable because of the fact that they are easier to manufacture and to maintain and allow easier adjustment of the degree of prevention. of liquid leakage or the amount of leakage. Auxiliary rollers 20 24 maybe smooth-surfaced metal rollers of uniform diameter, but a better effect can be obtained by using elastic rollers, e.g., rubber rollers. In case liquid leakage prevention is imperfect, the auxiliary rollers 20 24 may be secured by springs or other means to perfect the seals. If the rollers are used for forming a liquid reservoir as in the present invention, a better effect is obtained than in the case of using a flat plate-formed accumulation because, in the former case, the rollers rotate while sealing the liquid and therefore produce less friction with the driving rollers. Further due to strong contact pressure between the auxiliary rollers and the driving rollers, the surfaces of the driving rollers are strongly squeezed to effect cleaning of their surfaces, so that no soiling or contamination is caused when the back of the sensitive material sheet is contacted with the driving rollers.

In the embodiment of FIG. 1, no auxiliary electrode roller is provided in the first inter-roller space 40 or in the last inter-roller space 41. This is because no liquid reservoir is produced in these parts. If a liquid accumulation is formed here, there is produced greater possibility of causing backflow of the developer into the prebath section or causing developer to flow into the cleaning section, when the sensitive material sheet is guided into the mechanism. Experimentally, it is found that no flow-out of the developer in the liquid reservoir is caused if the distance between the developing electrodes and the sensitive material sheet is on the order of 0.1 mm. Theoretical calculation discloses that the optimum distance between the electrode and the latent image bearing surface is equal to or around the thickness of the insulating coating bearing the latent image. Generally speaking, this thickness ranges from several to several 10 microns. From the practical point of view, however, such optimization is substantially impossible for many cases. Thus, 50 several hundred micron clearances are employed in practical development. Preferable range is 50 500 microns, or twice to 10 times as large as the coating thickness. When either surface of the electrode or image bearing surface is rough, the distance may be zero. If no liquid accumulation is provided in the first and last spaces 40 and 41 as shown in FIG. 1, usually no liquid flowout is caused if the sensitive sheet material is passed linearly. In case the liquid is brought into the cleaning section with advance of the sensitive material sheet even if no liquid reservoir is provided in the last space 41, it is advisable to provide an air discharge nozzle 36 at a location just beyond the final roller 18 to strongly blow air from said nozzle to prevent outflow of the developer, whereby it is possible to effect removal of the liquid while not directly contacting the developed image surface. In order to wipe away the carry-over developer on the backside of the sensitive material sheet, a flexible film 37 made of plastic or the like may be provided at the rearmost end of a developer retaining tank 38 so as to lightly wipe the backside of the sheet with said film.

To ensure perfect prevention of outflow of the developer from the developing section, it is advantageous to arrange the driving rollers not linearly but in an down wardly convex arcuate configuration. It was, however, experimentally found that it is more preferable to carry the sensitive material sheet along a passage which is as linear as possible from the standpoint of minimizing troubles such as scraping when the developing elec' trode rollers approach the latent image surface and to obtain an image of higher quality. Stable transport of the sheet material through developing mechanism can also be secured by having the sheet in curled relative to the active side thereof and by passing such sheet along a convex passage.

Numerals 25 29 indicate developer discharging nozzles which may be provided by forming small holes or narrow slits in cylindrical pipes. Numerals 30 34 denote guide plates attached to the nozzles to allow the liquid discharged from nozzles 25 29 to flow down along said guide plates. As will be seen in FIG. 1, these guide plates are disposed so as to extend through the narrow spaces between the developing electrode rollers. The liquid discharged from nozzles 25 29 is initially gathered in the wedge-shaped portions defined by the guide plates and the electrode rollers, so it drops uniformly to form a liquid reservoir, thus making it less liable to produce unevenness of liquid supply.

The liquid, which has been used for development, drops downwardly into and is stored in a developer retaining tank 38, from which it is removed through discharge port 39 by a pump (not shown) and circulated for reuse. The rate of flow from the developer pool and the rate of discharged liquid from nozzles are balanced.

The manner of fitting of the auxiliary rollers for liquid reservoir formation (termed reservation at many points in the specification) is best shown in FIG. 3 which is a sectional view taken along the line III-III of FIG. 1. As shown in FIG. 1, the auxiliary rollers 20 24 rotate in the direction opposite to that of the carrier rollers 3 by friction, so that the diameter of these rollers must be selected to be sufficiently small to keep them uncontacted with the back of the sensitive material sheet. Also, the diameter of each driving roller and the pitch of these rollers must be so selected that the auxiliary rollers are housed within the spaces between the respective driving rollers. The driving rollers 3-10 and the auxiliary rollers 24 are in contact with each other and reduce the leakage of developer therebetween. The mounting of these auxiliary rollers is shown in FIG. 3.

In the embodiment of FIG. 1, driving rollers 3 10 for carriage of the sensitive material sheet are provided in the same number as the developing electrode rollers 11 18, but it should be understood that they need not necessarily be the same in number or in diameter. It is possible to decrease the number of the developing electrode rollers and to increase the number of the auxiliary electrode rollers 35. In order to facilitate smooth carriage of the sensitive material sheet and to prevent it from hitting against the drive rollers due to curl on the sheet, endless belts may be provided on the carrier rollers. Such an example is shown sectionally in FIG. 4 corresponding to FIG. 2, where numeral 50 indicates the endless belts passed along both end portions of the drive rollers.

In FIG. 5 is shown an embodiment where the passage of the sensitive material sheet is downwardly convexed to insure perfect prevention of flowout of the developer. Reference numerals correspond to that of FIG. 1. In this embodiment, as will be noted, the number of the developing electrode rollers is decreased while the number of auxiliary developing electrode rollers is increased. In this case, it is desirable to provide a device for correcting the tendency of the sensitive material itself to have a convex curl. It is also possible in this embodiment to form a liquid reservoir even if the gap be tween the developing electrode rollers and the sensitive sheet surface is large. In the case of linear passage as shown in FIG. 1, such a gap must be a fraction of one mm or zero at the first and last rollers used for forming a liquid pool, otherwise the flow of developer therebetween causes the streaks on the image. In the embodiment of FIG. 5, the sensitive material is fed in the direction of arrow 1 and discharged in the direction of arrow 2. In this embodiment, inlet and outlet of the sheet are upward and such a trouble is eliminated.

In FIG. 6 is shown, in section, a part of still another embodiment, where only the condition of forming a liquid reservoir is shown. In this embodiment, the auxiliary rollers for forming a liquid reservoir are used as the sensitive material carrier rollers. Numerals I 3' indicate the driving rollers of which the shafts are secured to the side plates so that they are driven from the outside. Since these rollers l 3' are not contacted with the sensitive material sheet, they may be made of metal or insulating material such as rubber. Numerals 4' 7' denote rollers disposed between driving rollers l 3' so as to be driven through friction with the driving rollers. They are adapted to let the sensitive material sheet advance by holding it between them and the endless belts 12' passed along both edges of the developing electrode rollers 8 I1 and are also so arranged as to fill the spaces between the driving rollers to form a liquid reservoir.

As is seen from the above discussion, the present invention is characterized by a mechanism in which a developer is applied from above a sensitive sheet material having an electrostatic latent image formed thereon while carrying said sheet by holding it between rollers in which the spaces between the rollers are filled by auxiliary rollers arranged such that the developer is prevented from freely falling down once it is formed into a liquid reservoir defined by said rollers, and the sensitive sheet is passed through said reservoir. The resultant developed image is perfectly free of edge effect.

trailing and unevenness of development. It will be understood, therefore, that presence or absence of the endless belts or auxiliary electrode rollers is not directly related to the spirit of the present invention.

Numerous modifications of the invention will become apparent to one of ordinary skill in the art upon reading the foregoing disclosure. During such a reading it will be evident that this invention provides a unique electrophotographic developing method and apparatus for accomplishing the objects and advantages herein stated.

What is claimed is:

l. A method for developing an electrostatic: latent image characterized by passing an electrostatic latent image bearing sheet between a plurality of electroconductive rollers provided between a pair of side plates and a plurality of spaced driving rollers disposed in contact with and beneath said electroconductive rollers, the approximate ends of said electroconductive rollers and said driving rollers extending between said side plates, said driving rollers carrying said latent image bearing sheet by frictionally holding it between the driving rollers and said electroconductive rollers, applying liquid developer to said electrostatic latent image from above the electroconductive rollers, and providing in the spaces between said driving rollers other rollers which are disposed between both side plates so that the developer applied from overhead is prevented from freely falling down but is temporarily restrained in a liquid reservoir formed by said driving rollers and said other rollers, said liquid reservoir being formed over the length of the passage of said latent image bearing sheet, so as to effect development of the latent image when the sheet is passed through said reservoir of developer.

2. An apparatus for developing an electrostatic latent image comprising a plurality of electroconductive rollers provided between a pair of flat side plates and a plurality of spaced driving rollers disposed in contact with and beneath said electroconductive rollers, the approximate ends of said electroconductive rollers and said driving rollers extending between said side plates, said driving rollers carrying a latent image bearing sheet by frictionally holding it between them and said electroconductive rollers, means for applying developer from overhead the electroconductive rollers, and other rollers disposed in the spaces between said spaced driving rollers and between both side plates so that said other rollers contact said driving rollers, whereby developer applied from overhead is prevented from freely falling down but is reservoired in a liquid reservoir formed by said driving rollers and said other rollers, said liquid reservoir being formed over the length of the passage of said latent image bearing sheet, so as to effect development of the latent image when the sheet is passed through said reservoir of developer.

3. An apparatus as in claim 2 including means for powering said driving rollers so that they are rotated.

4. An apparatus as in claim 2 including means for powering said other rollers so that they are rotated.

5. An apparatus as in claim 2 where said plurality of electroconductive rollers and said plurality of driving are disposed along a downwardly convexed path so that as said latent image bearing sheet leaves said apparatus, the tendency for said developer to flow out of said apparatus is minimized. 

1. A METHOD FOR DEVELOPING AN ELECTROSATIC LATENT IMAGE CHRACTERIZED BY PASSING AN ELECTROSTATIC LATENT IMAGE BEARING SHEET BETWEEN A PLURALITY OF ELECTROCONDUCTIVE ROLLERS PROVIDED BETWEEN A PAIR OD SIDE PLATES AND A PLURALITY OF SPACED DIRVING ROLLERS DISPOSED IN CONTACT WITH AND BENEATH SAID ELECTROCONDUCTIVE ROLLERS, THE APPROXIMATE ENDS OF SAID ELECTROCONDUCTIVE ROLLERS AND SAID DRIVING ROLLERS EXTENDING BETWEEN SAID SIDE PLATES SAID DRIVING ROLLERS CARRYING SAID LATENT IMAGE BEARING SHEET BY FRICTIONALLY HOLDING IT BETWEEN THE DRIVING ROLLERS AND SAID ELECTROCONDUCTIVE ROLLERS, APPLYING LIQUID DEVELOPER TO SAID ELECTROSTATIC LATENT IMAGE FROM ABOVE THE ELECTROCONDUCTIVE ROLLERS, AND PROVIDING IN THE SPACES BETWEEN SAID DRIVING ROLLERS OTHER ROLLERS WHICH ARE DISPOSED BETWEEN BOTH SIDE PLATES SO THAT THE DEVELOPER APPLIED FROM OVERHEAD IS PREVENTED FROM FREELY FALLING DOWN BUT IS TEMPORARILY RESTRAINED IN A LIQUID RESERVOIR FORMED BY SAID DRIVING ROLLERS AND SAID OTHER ROLLERS, SAID LIQUID RESERVOIR BEING FORMED OVER THE LENGTH OF THE PASSAGE OF SAID LATENT IMAGE BEARING SHEET, SO AS TO EFFECT DEVELOPMENT OF THE LATENT IMAGE WHEN THE SHEET IS PASSED THROUGH SAID RESERVOIR OF DEVELOPER.
 2. An apparatus for developing an electrostatic latent image comprising a plurality of electroconductive rollers provided between a pair of flat side plates and a plurality of spaced driving rollers disposed in contact with and beneath said electroconductive rollers, the approximate ends of said electroconductive rollers and said driving rollers extending between said side plates, said driving rollers carrying a latent image bearing sheet by frictionally holding it between them and said electroconductive rollers, means for applying developer from overhead the electroconductive rollers, and other rollers disposed in the spaces between said spaced driving rOllers and between both side plates so that said other rollers contact said driving rollers, whereby developer applied from overhead is prevented from freely falling down but is reservoired in a liquid reservoir formed by said driving rollers and said other rollers, said liquid reservoir being formed over the length of the passage of said latent image bearing sheet, so as to effect development of the latent image when the sheet is passed through said reservoir of developer.
 3. An apparatus as in claim 2 including means for powering said driving rollers so that they are rotated.
 4. An apparatus as in claim 2 including means for powering said other rollers so that they are rotated.
 5. An apparatus as in claim 2 where said plurality of electroconductive rollers and said plurality of driving are disposed along a downwardly convexed path so that as said latent image bearing sheet leaves said apparatus, the tendency for said developer to flow out of said apparatus is minimized. 